composting temps

ofpeteAugust 25, 2014

In the thread about Azolla I noted that using it as a source of N for composting increased the pile temperature from the usual 110-120 degrees to 140-150. This morning a couple of spots in the pile are at 170. I fear all I am going to find in the center is ash before long. Should I break it down again and reconstitute as I did yesterday or will that just encourage it to get hotter? At least there should be no weed seeds in the finished compost, but is very hot too hot?

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Slimy_Okra(2b)

170 is good. I would turn it only when it begins to cool.

    Bookmark   August 25, 2014 at 12:51PM
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tropical_thought(San Francisco)

No matter how hot you can get in one area, there is always an outside area that the weed seeds will live. There are very hard to kill so I remove weeds before they seed. If they have seeds they go in the city wide compost pick up. That is another reason I would not buy compost from the city if they did sell it or give it away. I put all diseased plants and leaves in there also. Considering what I put in I don't want any of that back. All the good things go in my personal bins.

    Bookmark   August 25, 2014 at 5:28PM
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Kimmsr(4a/5b-MI)

Since few of the thermophilic bacteria that generate the high temperatures in compost can survive at temperatures above 160 degrees the time to turn a compost pile, to cool it down, is before the temperatures get that high. Optimal temperatures for hot composting are 135 to 140 degrees. 170 degrees is approaching the temperatures at which the compost pile could spontaneously combust.

    Bookmark   August 26, 2014 at 7:21AM
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ofpete

Thanks for that advice on temperature. I was wondering about the spontaneous combustion potential and am going to bust down the pile and let it cool down a bit. Maybe add more cellulose like fine wood chips?

    Bookmark   August 26, 2014 at 11:02AM
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ofpete

Thanks for that advice on temperature. I was wondering about the spontaneous combustion potential and am going to bust down the pile and let it cool down a bit. Maybe add more cellulose like fine wood chips?

    Bookmark   August 26, 2014 at 11:03AM
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tropical_thought(San Francisco)

There was a thread about spontaneous combustion a while back, try to look for that one. It seems to not happen very often. At first I thought, oh it would be awful if someone's house burned down due to composting, but then I was like it happens so infrequently, it is like seeing Big Foot. So not much of a problem.

    Bookmark   August 26, 2014 at 11:32AM
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ofpete

Well, I broke the pile down and let it sit for about an hour and then reconstituted it, adding fine wood chips and dead live oak leaves to the mix and sprinkling with water. Two hours later the temp is not quite 130, so I guess it has lost the ardor it used to have. Maybe it is that added carbon.

    Bookmark   August 26, 2014 at 4:47PM
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ofpete

Well, I broke the pile down and let it sit for about an hour and then reconstituted it, adding fine wood chips and dead live oak leaves to the mix and sprinkling with water. Two hours later the temp is not quite 130, so I guess it has lost the ardor it used to have. Maybe it is that added carbon.

    Bookmark   August 26, 2014 at 4:50PM
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toxcrusadr

I've had compost go up to 180F before. Not on purpose, mind you, but I used too much high N material. This was years ago before I knew as much as I do now. If it happened today I'd add some browns to get it down in the ideal range. However, I can tell you that I did get compost in the end, so it's not the end of the world. Also, it did not catch on fire or turn to ash.

Theoretically, combustion requires much higher temperatures. However, compost piles can and do spontaneously combust. It's rare when you consider the amount of composting that actually goes on. It usually happens in large industrial piles that are not managed properly. I wouldn't lose too much sleep over it. Control your temps because you want better quality compost. :-]

    Bookmark   August 26, 2014 at 5:12PM
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ofpete

Thanks Tox for some good and interesting information. This morning the pile is back up to a little over 140, so by doing just what you said, adding carbon in the form of dry wood chips and oak leaves for a better C/N ratio it seems to be settling down to doing a more moderate job of composting.

I was not that afraid of spontaneous combustion since no structures would have been threatened - just didn't want to see all my hard work go to ash and those nutrients go up in smoke.

But this much I have learned: that Azolla is a HUGE source of N if allowed to dry and then shredded before adding to the heap.

    Bookmark   August 27, 2014 at 10:55AM
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Kimmsr(4a/5b-MI)

Spontaneous combustion of compost piles is more common then many think. Temperatures between 150 and 200 degrees are enough to start the fire. I understand that many people doubt that can happen because they have not seen it, but it can and does happen. This is kind of like the 6 blind men describing an elephant.

Here is a link that might be useful: Spontaneous Combustion of compost

    Bookmark   August 27, 2014 at 11:19AM
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toxcrusadr

Which is why I said 'theoretically they shouldn't, but it can and does happen.' My theory is that temperature can exceed the 'bulk' temperature on a microscopic scale, and all it takes is a pinpoint of runaway oxidation. Same as in a bucket of oily rags supposedly at room temperature.

    Bookmark   August 27, 2014 at 12:26PM
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Lloyd

Kimm says "Temperatures between 150 and 200 degrees are enough to start the fire."

The link says "composting materials ignite at temperatures between 150 and 200ðC."

What was left out was the "C" part. That is Celsius my friend. Convert to Fahrenheit and you get 302-392 degrees. I'd not panic about hitting 165F, done it lots of times.

Lloyd

    Bookmark   August 27, 2014 at 5:44PM
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Slimy_Okra(2b)

If thermophilic bacteria cannot tolerate a temperature of 170 degrees F, they are not really thermophilic. Or to be more accurate, there are different groups of thermophiles, and some not only tolerate but thrive at temperatures above 180 degrees F. Secondly, assuming the compost got hot enough to kill (some or most of) them off, this would create a negative feedback effect and cool the compost pile on its own. Even if all the mesophiles and lower-range thermophiles were killed off, they will soon recolonize the pile. These and the remaining bacteria would become active again, thus heating the compost pile again, and so on. I stand by my original statement - there is no need to worry about an excessively hot compost pile. Just let it run its course and be happy that you're destroying a whackload of weed seeds in the process.

Keep in mind that water boils at 212 degrees F, and organic materials combust at temperatures much higher than the boiling point of water. Toxcrusadr does have a point in that tiny pockets of the pile may superheat well above this point and ignite gases, but the chances of this happening are very, very low.

This post was edited by Slimy_Okra on Wed, Aug 27, 14 at 19:16

    Bookmark   August 27, 2014 at 7:10PM
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Kimmsr(4a/5b-MI)

I did miss the "C" for centigrade. However, as the authors of the article state spontaneous combustion of compost piles is more common then most people think. To state that there is no need to worry about an excessively hot compost pile is irresponsible at best.

    Bookmark   August 29, 2014 at 7:32AM
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Allen456(8)

Spontaneous combustion mulch fire as we speak (type).

Link attached.

Here is a link that might be useful: Mulch fire burning in Barrow Co. for the past week

    Bookmark   August 29, 2014 at 7:34AM
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Lloyd

"To state that there is no need to worry about an excessively hot compost pile is irresponsible at best."

We've been down this road so many times kimm, I would have thought you'd give it up. The problem arises when people exagerate what an excessivley hot pile is. And you sir, have a reputation for exaggeration that is well documented. No one has to worry about a backyard compost pile at 165F self combusting.

Large piles of organics as in the link from Allen456 have the potential to self-combust. Large pile fires are well documented. Everyone acknowledges this. Backyard piles at 165F? Ya, not so much.

Lloyd

    Bookmark   August 29, 2014 at 8:47AM
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Kimmsr(4a/5b-MI)

In my years as a firefighter I have been on a few fires caused by self igniting compost piles and in the fire investigation schools I have attended this possibility of spontaneous combustion of compost piles and other piles of organic matter was discussed. Conversations with firefighters from all over the USA and Canada tell me this is not an isolated phenomena.
News reports of this occurring also tells me this is not a very rare phenomena either. That spontaneous combustion of compost can occur is something people should be aware of and hiding ones head in the sand will not make that fact go away.

    Bookmark   August 30, 2014 at 7:11AM
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davids10 z7a nv.

when i make my pile it usually goes to between 172 and 176 for the first heating. after each mixing the heat is less. at 140 i let it go to cooling at which point its finished. as for spontaneous combustion, those heaps are usually enormous-commercial compost makers or sawdust heaps at lumber mills,

    Bookmark   August 30, 2014 at 11:04PM
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InTheADK

We had a fire locally that was the result of spontaneous combustion of compost last summer. The guy cut his lawn and threw all of the clippings into his container (no mixing). Container was attached to the house, but luckily no one was hurt. I think you have to use SOME common sense.

    Bookmark   August 31, 2014 at 4:20PM
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toxcrusadr

Yes, you do. The logical fallacy here is that counting news accounts of flaming compost piles gives you a number, but offers no comparison to the total population - i.e. the number of compost piles. You have no reference to how many did NOT catch fire, or what percentage of the total DID catch fire.

Obviously it happens, I suspect the chance of it happening to any one pile is very very small, AND common sense should be used.

I have probably made hundreds of compost piles and batches in my career. I know dozens of people who also garden and compost. Yet none of us have ever seen or heard a first hand account of one catching fire. I would estimate it's on the order of a 1/10% chance for any given pile.

When I give composting workshops I always recommend not putting the compost right next to the house. It's mostly for insect and potential odor issues, and I don't even mention fire so as not to freak out the novices.

    Bookmark   September 2, 2014 at 1:11PM
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Lloyd

Also keep in mind the inherent inaccuracy of news reports. I've read aviation stories that I am intimately familiar with that the media just butchers so I have little faith in them even being 50% accurate. Furthermore, just how much investigation do people think goes into a small organics fire? I suspect, unless it involves a substantial structure, or the owner admits to a reason (smoking, equipment, etc), the report takes the easiest path and that would be "spontaneous combustion".

As an example, a local firefighter's house burnt down because his wife 'extinguished' her cigarette in a potted plant on the deck. She admitted it, otherwise who knows how it would have been classified.

Lloyd

    Bookmark   September 2, 2014 at 1:56PM
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ofpete

Now when I turn the pile I am finding large volumes of dry gray stuff, looking almost like ash, though individual small leaves are still intact. The pile temps have been ranging between 120-140, so it should be doing what it is supposed to do, but is this a normal aspect of the composting cycle and that eventually everything will come back to being dark and crumbly, or has it been "burned" too badly?

    Bookmark   September 11, 2014 at 12:53PM
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drmbear

I find this in areas of my piles that were working well, very hot, and then dried out. Not really something to worry about - just turn it and moisten it as you remake the pile.

    Bookmark   September 11, 2014 at 3:23PM
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floral_uk z.8/9 SW UK

The grey stuff is fungus, not real ash. I find it in my compost heaps and I've never had, or tried to have, a hot pile in many years of gardening.

Here is a link that might be useful: Ash-like stuff in compost heaps.

    Bookmark   September 11, 2014 at 4:29PM
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Kimmsr(4a/5b-MI)

It could be ash or it could be a fungus, although the two do not look anything alike. The ash will be dry and powdery while the Fungus mycelium will be moist and sticky. The ash, often, will still look like the material it was, ie. a leaf and be grey while the fungi will have grown on the material and that material will be a dark brown, not grey color.

    Bookmark   September 12, 2014 at 5:52AM
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toxcrusadr

I have seen exactly the conditions described in the linked thread, an ashy looking layer 6-12" below the top of a hot pile. There is no charring or black material, only the gray powdery stuff. It's not moist because the heat of the pile has actually dried it out, at least when I've seen it. If it was ash there is no visible reason why the combustion did not continue as there is dry material above and below. Therefore, I too think it is fungi or actinobacteria.

It would be quite simple to verify with a microscope or a couple of simple lab tests.

    Bookmark   September 12, 2014 at 10:52AM
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ofpete

Definitely not a fungus, since the stuff is bone dry and, as I had noted, some small leaves remained intact but as if they had ignited - retaining their shapes though. My concern is that wherever it looks like that all the biota have been destroyed, so that microbial action can no longer happen, and has it lost all nutrient value. This morning repeated jabs with the thermometer show readings of right around 130, so maybe things are slowing a bit and I'll be seeing more normal activity.

    Bookmark   September 12, 2014 at 11:51AM
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